This section is intended to provide a background or context for the invention to be disclosed below. The description to follow may include concepts that could be pursued, but have not necessarily been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated below, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
A filter is composed of a number of resonating structures and energy coupling structures which are arranged to exchange radio-frequency (RF) energy among themselves and input and output ports. The pattern of interconnection of these resonators to one another and to the input and output ports, the strength of these interconnections, and the resonant frequencies of the resonators determine the response of the filter.
During the design process for a filter, the arrangement of the parts, the materials from which the parts are made, and the precise dimensions of the parts are determined such that an ideal filter so composed will perform the desired filtering function. If a physical filter conforming exactly to this design could be manufactured, the filter would perform exactly as intended by the designer.
However, in practice, the precision and accuracy of manufacture of both the materials and the parts are limited, and results in errors in resonant frequencies and coupling strengths, which, in turn, cause the filter response to differ from that predicted by an ideal filter model. Often, this departure from the ideal response is sufficiently large to bring the filter outside of its design specification. Because of this, it is desirable to include in the filter design some means for adjusting the resonator frequencies and coupling strengths to bring the filter response within the design specification.
A common means for accomplishing this is to include, in or on the filter, tuning screws or other devices, which are well known in the art. An alternative means often used with small ceramic monoblock filters is to remove selected portions of the metallization from their exteriors, and possibly portions of ceramic as well, to perform the tuning.
Most filters are manufactured as completed units and, subsequent to their manufacture, the tuning procedure is performed on the entire filter. Since various adjustments on the filter may interact strongly with one another, the tuning procedure is often quite complicated, and requires a skilled operator.
An alternative tuning method is to build the filter parts separately, to tune them individually to a specification calculated for the separate parts from the ideal filter model, and finally to assemble them to form the filter. Since the individual parts are simple compared with the fully assembled filter, the tuning procedure for the individual parts can also be made very simple. This minimizes the need for skilled operators to tune the filters. Such a procedure also provides the benefit of either reducing or entirely eliminating the tuning process for the assembled filter.
In many cases, it is sufficient only to adjust the resonant frequencies of the resonator parts, because the manufacturing precision and accuracy for the resonator parts are good enough to bring the coupling strengths within the range required to enable the performance of the assembled filter to be within specification. In such cases, adjustment of the resonant frequencies is all that is required to tune the individual parts. In other cases, the manufacturing precision and accuracy is insufficient to bring the coupling strengths within the required range, and so the couplings between the individual parts must also be adjusted to bring the assembled filter within specification.
To facilitate pretuning of the frequencies of the individual parts, both methods of measurement of the frequencies and methods of adjustment of the frequencies are required. Likewise, to allow pretuning of the couplings between adjacent parts, both methods of measurement of the couplings and methods of adjustment of the couplings are required.
In a filter constructed from separate resonator parts joined together, the coupling between adjacent resonator parts often takes the form of a coupling structure shared between the adjacent parts. In order to measure the coupling strengths between the resonator parts, it is necessary, prior to the measurement, to bring them together either as the entire set of parts so as to assemble the entire filter, as a subset of parts so as to assemble only part of the filter, or as a pair of adjacent parts between which is the coupling strength to be adjusted. In order to adjust the coupling strengths, some procedure for modifying the coupling structure or some sort of tuning structure must be present, either as an explicit feature of the coupling structure, or as an additional structure which can be added to the coupling structure as part of the tuning process.
A tuning method for either frequencies or coupling strengths may include the manipulation of a tuning device or structure included as part of the resonator or coupling structure, such as a tuning screw or deformable metal part. Alternatively, a method may comprise an operation performed on the resonator or coupling structure, such as the removal of material from a selected region, or the addition of material to a selected region. The method may also comprise a combination of these, or any other means or process which can alter the resonant frequencies of the resonator part or which can alter the coupling strengths between adjacent resonator parts.
A tuning physical adjustment (commonly abbreviated more simply as “adjustment”) can then be defined as one or more manipulations of tuning structures and/or one or more operations causing one or more of the resonant frequencies or coupling strengths to be altered. For instance, such physical adjustment includes, but is not limited to, removal of material from a surface or face of a resonator component; drilling of holes in the resonator component; addition of material, such as silver, to a surface or face; addition of material, such as silver, to a hole or holes; adjustments of screws in the resonator component; and/or denting of material covering the resonator component.
What is needed to enable the part to be frequency tuned is an adjustment or adjustments which can alter the resonant frequency of the part by a sufficient amount to bring a typical manufactured part within specification.
What is needed to enable the coupling strength between adjacent pairs of parts to be tuned is an adjustment or a set of adjustments which can alter the coupling strength by a sufficient amount to bring the coupling strength between a typical adjacent pair of manufactured parts within specification.